_The Genito-urinary System._—The dark colored urine is pathognomonic of the disease and gives it its name. The reddish to almost black color is due to haemoglobin and not to bile. Bile pigments do not appear in the urine. There is but rarely a red cell to be found in the granular débris with occasional haematoidin crystals which forms the urinary sediment, hence it is haemoglobinuria and not haematuria. The urine resists decomposition for a long time. Albumin is present in large amount and comes on with the onset of haemoglobinuria. Casts are abundant and urobilinuria is marked. As a result of the blocking up of the renal tubules with haemoglobin casts pain over the loins and anuria may occur. There may be vesical tenesmus. _The Blood._—Cases have been reported where as many as 2,000,000 red cells have been destroyed within twenty-four hours, so that rapid and marked anaemia characterizes the disease. The blood is thin and the serum tinged. The degenerative changes of the red cells are not as commonly seen as one would expect but this is probably due to the fact that degenerated cells are first destroyed in the excessive haemolysis. Hb percentage reduction generally parallels the reduction in red cells. Melaniferous leucocytes may be found and during the leucopenia, which follows the paroxysm, the large mononuclears and transitionals may be increased to 20%. There is a reduction in the alkalinity and coagulability of the blood. DIAGNOSIS =Clinical Diagnosis.=—An unusually asthenic prostrating paroxysm, similar to that of a malarial chill, but with more intense rigor, during which haemoglobinuria, early jaundice and marked bilious vomiting are features, makes for a diagnosis of blackwater fever. The two diseases which are most likely to be confused with blackwater fever are yellow fever and bilious remittent malarial fever. In infectious jaundice the jaundice does not appear for 48 to 72 hours, the pulse is slow, there is no haemoglobinuria, although there may be a haematuria, and we have a polynuclear leucocytosis. A case of paroxysmal haemoglobinuria occurring in a blackwater district would be impossible to differentiate from a very mild case of blackwater fever. Chlorate of potash or carbolic-acid poisoning, or snake bite, or severe burns, may produce haemoglobinuria.